I'll second Grim's advice about considering a used touring bike. I have a '92 Cannondale T600 I use for my half century commute and it handles it extremely well. It's pushing 89k miles these days (gotta hit that magic 88,888 on the odometer first :-). I found the same bike on ebay a few years ago for $300 for my son. With a supposed 5k miles on it by the original owner, it should have a lot of life left in it.

I've been upgrading the components as they wear out, usually by stock piling clearance items when new stuff gets introduced. It's currently at the (9 spd) Ultegra/XTR/XT level.